1. Field of the Invention
This invention relates to apparatus and method for photometrically analyzing in batch type determinations the rate or end point of a chemical reaction for quantitation of a constituent of interest in a sample, usually blood serum.
2. Prior Art
Heretofore, manufacturers of fully automated photometric analyzers of the type designed to perform batch type enzyme quantitations of blood serum by kinetic or reaction rate measurements have sought unsuccessfully in moderate cost equipment to increase the number of samples analyzed per hour with reference to these temperature-and-time dependent reactions. This has posed the problem of getting the samples up to the proper temperature for the reaction and maintaining this temperature within very exacting, fine tolerances during the period of optical measurement, without contamination of sample. This problem may be termed one of sample incubation. For example, in the analysis of the enzyme CPK in blood serum it has been found that the concentration as determined by optical density may be off by as much as 8% for a deviation of 1.0.degree.C from the set temperature such as 30.degree.C or 37.degree.C, for example. Exaggerated claims have been made by manufacturers concerning the fineness of the temperature regulation of sample in automated and semi-automated kinetic analyzers.
For diagnostic use in hospitals and laboratories where space is at a premium, it is desirable to automatically quantitate 30 or more samples an hour. It takes approximately 15 minutes supported in a cuvette in an air bath to bring the temperature from 4.degree.C up to the temperature of 37.degree.C of the liquid contents of approximately 1.5 ml of the cuvette. The cuvette with its serum sample, either with its reagents in freeze-dried condition or reconstituted condition, may have been taken from a refrigerator a short time before. An air bath of such loaded cuvettes is preferred to a water bath for optical reasons despite the advantage of the latter in tending to approach matching indexes of refraction and bring the liquid contents of the cuvette up to temperature in approximately 6 minutes if the water of the bath is well circulated. Such disadvantages are that the water of the bath requires replenishment from time to time, which may be overlooked by the operator. If the water level falls below the analyzer's viewing area, the analytical results are invalidated. Further, the bath water may have its temperature changed on replenishment. It may contain dirt which drifts between the optical window of the analyzer making it appear falsely to the photodetector, which detects change in the optical density of the sample mixture, that a change or shift in optical density has begun. Still further, impurities in the bath water coat such windows after a period of time and, hence, interfere with analysis. The use of such bath water is also cumbersome and inconvenient. On the other hand, if an equipment manufacturer relies solely on utilization of an air bath to reach and maintain a proper reaction temperature, at least initial severe and undesirable temperature gradients are established in the liquids and in the material of which the cuvette is structured, usually plastic. At least one manufacturer has attempted to avoid these problems by utilizing a closed pouch for the sample-reagent materials which are brought up toward design temperature by electrically heated plates placed temporarily in contact with the sides of the pouch. Such practice is open to the objection that the temperature of the liquid within the pouch is not sensed by a sensor inserted therein, and such plates may develop hot spots leading to the aforementioned undesirable temperature gradient.
In such kinetic determinations, the viewing area of the reaction within the cuvette must not be obscured by a temperature sensor. Yet, it is in this area that the temperature of the reaction mixture is most critical as the temperature of the liquid in another portion of the cuvette may be off by a few tenths of one degree, enough to invalidate many analyses if the total deviation is more than 1.0.degree.C from the design or set temperature of 37.degree.C or 30.degree.C, for example. Another restriction in such analysis is that any temperature-sensing probe immersed in the liquids of cuvettes successively must not contaminate, by sample and/or reagent carryover from one cuvette to the next, the reactants. Further, as far as is known, no automated kinetic analyzer has existed heretofore which goes beyond the sample liquid temperature-regulating limitations of the equipment design in computing the constituent concentration, that is, to the estimated real temperature at the time of the optical determination for inclusion in the concentration determination.
The present invention seeks to overcome these difficulties with the prior art.